The invention concerns an adjusting drive for radially adjusting the cutting edge of a tool.
Radial adjustment of the cutting edge of tools serves to compensate for the wear of the cutting edge and to lift the cutting edge from the surface of the workpiece being machined at the end of a machining process, prior to the onset of the return motion of the tool. In a tool of this type, the cutting edge is radially displaceable in the body of the tool by means of a connecting rod. The latter is axially movable in a rotatingly driven tool spindle. A rotatable adjusting piston is axially displaceable in the housing of the adjusting drive and connected by means of an axial bearing with the connecting rod, and with a servomotor arranged in an axially parallel manner with respect to the connecting rod. The output shaft of said servomotor is connected with the adjusting piston by means of a screw and a spindle screw nut.
In order to obtain a degree of adjustability of the cutting edge, the tool equipped with the edge, for example a boring bit, may be mounted on a swiveling and/or elastically deformable part of the body of the tool. The conversion of the axial motion of the connecting rod into the radial motion of the cutting edge takes place in most cases by means of an inclined surface provided on the connecting rod, which supports the moving part of the tool body as disclosed in German OS No. 24 05 694, the disclosure of which is hereby incorporated by reference herein.
If several cutting edges are arranged in one tool body, it is desirable to have all or at least several cutting edges adjustable, as it is not rational to extend only the life of a single cutting edge by compensating for tool wear, since the overall life of the tool is determined by the uncompensated wear of another cutting edge of the tool.
However, the use of several, coaxially arranged connecting rods is difficult, because a separate adjusting drive must be provided for each of the connecting rods. It is known from French Pat. No. 2,327,840 to provide a hollow screw in an adjusting drive of the aforementioned type, so that one or several connecting rods may be arranged coaxially and each connected with a separate adjusting drive arranged therebehind.
Because of the relatively great structural length of the known adjusting drive, the overall length of several adjusting drives arranged axially following each other would be excessively large. This would create particular difficulties for the innermost and therefore thinnest and longest connecting rod.
In the known adjusting drive, the screw nut surrounding the hollow screw is located within the axial bearing supporting the screw nut, which therefore must have a relatively large diameter. The threaded nut arranged coaxially with respect to the connecting rod is effected by means of the servomotor through a bevel gear drive, the servomotor being arranged in an axially parallel manner. The relatively large axial structural length of the known adjusting drive results, in particular, from the fact that (i) the spindle nut, (ii) the rotationally stationary guide of the screw and (iii) the axial bearing connecting the screw with the connecting rod, are arranged following each other in the axial direction.
It is an object of the present invention to provide an adjusting drive of the aforementioned type, having the shortest axial structural length possible. Advantageously, a plurality of such adjusting drives may be arranged following each other in succession, without excessively extending the overall structural length of the assembly.